U.S. Pat. No. 3,646,155 discloses that a silane-modified ethylene-type resin which has been produced by reacting certain silane compounds with an ethylene-type resin (such as polyethylene, a copolymer consisting primarily of ethylene, etc.) in the presence of a free-radical-producing agent can be cross-linked by exposure to water in the presence of a silanol-condensation catalyst. Silane-modified ethylene-type resins obtained by this method can have their cross-link density changed at will, and have excellent properties of heat-resistance, atmosphere-resistance and chemical resistance; as a result, they are used in the manufacture of pipe, electrical insulation, film, etc. and are also ideal in the manufacture of foamed articles.
However, the aforementioned silane-modified ethylene-type resin absorbs moisture from the atmosphere and the cross-linking reaction gradually proceeds, even in the absence of a silanol-condensation catalyst. As a result, the melt index falls and moldability decreases. Because of these defects, it has been necessary to adopt special storage methods in order to suppress the aforementioned change with the passage of time in the case of long-term storage.